This invention relates to an electric machine, and more particularly, to a hybrid electric machine including a pair of rotors and a single toroidally wound stator, and which generates flux by way of a plurality of permanent magnet poles, a plurality of consequent poles, and a selectively controllable field current.
Electric machines such as generators and motors generally utilize a plurality of rotating magnets and/or rotating magnetic members in order to generate electrical power and/or torque.
One common type of electric machine, known as an electromagnetic motor or generator, generally includes a rotor having a plurality of pole fingers in the form of north and south ferromagnetic members or consequent poles, and one or more electric xe2x80x9cfield coilsxe2x80x9d which are selectively and electrically energized, thereby selectively producing a flux within the rotating members of the rotor. In these types of electromagnetic machines, electric power is supplied to the rotating field coils by way of one or more brushes, slip rings, and/or other devices. The output of these electromagnetic machines (e.g., the output torque, power, or voltage) can be relatively easily controlled by controlling the amount of current supplied to the xe2x80x9cfield coilsxe2x80x9d. In this manner, these types of electric machines can provide a relatively constant output voltage, torque, or power over a relatively wide range of operating speeds and temperatures. While these electromagnetic machines are effective to generate a relatively constant output torque, power, or voltage, they suffer frog some drawbacks.
For example and without limitation, the brushes, slip rings, and/or other devices, which are required within these machines to provide an electrical connection to the rotating field coils, add to the cost, complexity, and size of the machines, and undesirably wear over time, thereby resulting in diminished performance and/or failure of the machine.
A second type of electric machine, known as a permanent magnet motor or generator, generally includes a rotor having a plurality of permanent magnets which selectively produce a flux within the machine. Due to the permanent magnets within the rotor, these types of machines do not require field coils to produce magnetic flux. Therefore, these systems do not require the brushes, slip rings and other devices which are necessary in the previously described electromagnetic machines. As such, these permanent magnet machines are typically smaller, less complex, more efficient, and less costly than the previously described electromagnetic machines. These permanent magnet machines do, however, suffer from some other drawbacks.
Namely, because the flux in these electric machines is provided by permanent magnets, it remains substantially constant and is relatively difficult to temporarily alter or vary by use of electric field coils. Thus, the output of these machines (e.g., the output torque, power or voltage) is almost solely and completely dependent upon the operating speed of the machine. As such, these machines provide a relatively constant output voltage, torque, or power only over a relatively narrow and limited range of operating speeds, and therefore cannot be utilized in applications where the operating speed is provided by a relatively xe2x80x9cvariablexe2x80x9d or fluctuating source, such as the engine of a vehicle.
Attempts have been made to provide electric machines which generate flux through permanent magnets and xe2x80x9csoftxe2x80x9d magnetic members. For example and without limitation, one such type of electric machine includes a pair of stator assemblies, a disc-shaped rotor having a plurality of permanent magnets and soft magnetic portions, members or consequent poles, and a stationary field coil which is used to selectively vary the flux generated by the consequent poles, thereby desirably controlling and/or maintaining the output torque, power, or voltage at a desired magnitude over a relatively wide range of operating speeds. While this type of electric machine is effective to provide a controllable and relatively constant output power and/or voltage, it employs two separate stator assemblies each comprising a separate and independent winding. These separate windings require a relatively significant and costly amount of copper wire and are independently controlled, thereby undesirably increasing the cost and complexity of the machine.
There is therefore a need for a new and improved electric machine which overcomes many, if not all, of the previously delineated drawbacks of such prior electric machines.
It is a first object of the invention to provide an electric machine which overcomes at least some of the .previously delineated drawbacks of prior electric machines.
It is a second object of the invention to provide an electric machine which provides a relatively constant output power and/or voltage over a relatively wide range of operating speeds.
It is a third object of the invention to provide an electric machine having a torque, power, and/or voltage output which may be substantially and selectively controlled by a way of one or more stationary field coils, and which employs a single stator assembly.
It is a fourth object of the invention to provide an electric machine having a pair of rotors which each include a plurality of permanent magnets and consequent poles.
According to a first aspect of the present invention, an electric machine is provided and includes a pair of rotors which are rotatably disposed upon a shaft. Each of the rotors has a plurality of permanent magnets which collectively generate a first magnetic flux and a plurality of consequent poles which collectively generate a second magnetic flux. A stator assembly is fixedly disposed between the rotors, and has a winding and a core. The electric machine further includes at least one coil which is fixedly disposed in relative close proximity to the rotors and which is selectively energizable, the energization being effective to controllably vary the second magnetic flux.
According to a second aspect of the present invention, a method for providing an electric machine having a controllable output voltage is provided. The method includes the steps of providing a housing; providing a pair of rotors having a plurality of permanent magnets which provide a first magnetic flux and a plurality of consequent poles which provide a second magnetic flux; rotatably disposing the rotors within the housing; providing a stator having winding; disposing the stator between the pair of rotors; fixedly coupling the stator to the housing; providing at least one field coil; fixedly disposing the at least one field coil in relatively close proximity to the rotor; selectively rotating the pair of rotors effective to produce an output voltage having a magnitude within the winding; and selectively energizing the at least one field coil, effective to vary the second magnetic flux, thereby controlling the magnitude of the output voltage.
These and other features, aspects, and advantages of the invention will become apparent by reading the following specification and by reference to the following drawings.